Missouri Attorney General Chris Koster has not said whether he will fight the Obama administration’s carbon limits, but the state’s utilities are encouraging him to mount a legal challenge.

A group including the chief executives of Ameren Corp., Great Plains Electric and Empire District Electric sent Koster a letter Monday urging him to join other states that are taking legal action against the president’s Clean Power Plan, the first set of federal regulations aimed at lowering carbon dioxide emissions.

“One clear challenge to EPA’s (Clean Power Plan) is that it has significantly overreached its authority granted under the Clean Air Act,” the utilities wrote in their letter to Koster.

Many Democrats support the proposed carbon rules, but Koster, the Democratic frontrunner for Missouri’s 2016 gubernatorial race, has yet to state his position.